Guide to Marginal Propensity to Save (MPS)

By Ashley Kilroy · August 15, 2023 · 9 minute read

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Guide to Marginal Propensity to Save (MPS)

The marginal propensity to save (MPS) is an economic concept that says when a person’s income rises, the MPS will determine the amount of money that is saved vs. spent on goods and services. This is an element in Keynesian Economic Theory, and it can have an important impact. The MPS can enable economists to figure out how to spend either government dollars or private funding.

But does MPS impact the average individual’s savings account? It can be a useful notion, and in this article you will learn:

•   What is marginal propensity to save (MPS)?

•   Why does MPS matter?

•   What does MPS mean to the average person?

The Keynesian Economic Theory, Explained

Economist John Maynard Keynes published The General Theory of Employment, Interest, and Money, or simply as The General Theory, in 1936. This text changed economic thought from that point on and is known as one of the classic economic publications. In the book, Keynes tried to explain economic fluctuations, especially the ones seen in the Great Depression of the 1930s.

Essentially, The General Theory was built on the idea that as a result of inadequate demand for goods and services, recessions and depressions could occur. Keynes’ theory was not just for economists—it was intended for policymakers worldwide. Keynes advocated for an increase in government spending, which would boost the production of goods and services to minimize unemployment rates and enhance economic activity. In general, this theory went against the traditional economic policy of laissez-faire, which requires minimal government involvement.

There are three main elements of this theory. These elements include:

Aggregate demand: This is the demand influenced by the public and private sectors. The level of demand in the private sector may impact macroeconomic conditions. For instance, a lull in spending may bring an economy into a recession. At this point, the government can intervene with monetary stimulus.

Prices: Wages, for example, are often slow to respond to supply and demand changes. This may result in an excess or shortage of labor supply.

Changes in demand: Any change in aggregate demand results in the most considerable impact on economic production and employment. The theory states that consumer and government spending, investments, and exports increase output. Therefore, even a change to one of these factors and the output will change.

The Keynesian Multiplier was created as a result of the change in aggregate demand. The Keynesian Multiplier states, “The economy’s output is a multiple of the increase or decrease in spending. If the fiscal multiplier is greater than 1, then a $1 increase in spending will increase the total output by a value greater than $1.”

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Calculating Marginal Propensity to Save

The Keynesian Multiplier value relies on the marginal propensity to save (MPS) and the marginal propensity to consume (MPC). Here’s how you can calculate the marginal propensity to save.

Marginal Propensity to Save Formula

When people receive additional income, the MPS is the change in the savings amount. If their income increases, the MPS measures the amount of income they choose to save instead of spending it on goods and services.

That said, this is how to calculate MPS: MPS = change in savings / change in income.

For example, let’s say someone received a $1,000 raise. Of that $1000 increase in income, they decide to spend $300 on new clothes, $200 on a fancy dinner out, and save the remaining $500, so the MPS is 0.5.

(1000 – 300 – 200) / 500 = 0.5

Marginal Propensity to Consume

Conversely, the MPC is the change in the spending, or consuming, amount. If someone’s income increases, the MPC measures the amount of income they choose to spend on goods and services instead of savings.

With this in mind, MPC is calculated as MPC = change in consumption / change in income.

By using the example above, the MPC would be 500 / 1000 = 0.5.

According to Keynesian economic theory, when production increases, the level of income rises too, triggering an increase in spending.

Marginal Propensity to Save Example

As mentioned above, the marginal propensity to save can be illustrated by someone getting a raise. If you receive a $5,000 raise and decide to spend $2,500 on a vacation and save the other half.

The MPS would be change in savings / change in income, or $2,500 / $5,000, or 0.5.

Top 3 Factors That Influence Saving

Knowing how to find MPS and MPC may seem pretty straightforward. However, both calculations only account for the excess of disposable income; the calculations don’t account for other factors that may influence a consumer’s consumption functions. If one of these non-income factors shifts, the entire consumption function may shift.

Here are some of the non-income factors that may influence a consumer’s consumption function.

1. Wealth

Wealth and income are two different variables in economics. For example, suppose Javier has a job earning $60,000 per year. If his aunt Ines passes away and leaves him $200,000 as an inheritance, his income is still $60,000 per year, but his wealth has increased.

Similarly, if Javier owns a piece of art that increases in value or his investment portfolio grows, his wealth has also gone up. Just because his wealth increases doesn’t mean his income does as well.

Therefore, an increase in wealth may increase consumption despite income levels staying the same. However, both the consumption and savings function may shift upwards as well because of the newfound wealth. The same is true in the opposite situation. If wealth decreases, the consumption and savings functions may decrease as well.

2. Expectations

In some cases, consumers may adjust their spending habits based on the expectation of future income coming their way. Expectations change the shift in consumption and savings functions because there is no change in actual income, just how it’s being spent.

For example, suppose Naomi assumes her income is going to increase soon. She may consume more now because of her expectation that her income is about to grow. This may highlight an upward shift in the consumption function without an increase in income.

On the other hand, if Naomi were pessimistic about her future income, such as the fear of losing her job, she may decrease her consumption without dropping her income. This scenario may also shift the consumption factor.


Consumers may also adjust their consumption and savings if they’re in debt. It’s observed that in economies where consumer debt rises, savings go up while consumption goes down. There is a level of debt when consumers typically feel uncomfortable spending more. Even if their income remains the same, if too much debt plagues their pocketbooks, they will start to save more and spend less so they can pay off their debt.

Conversely, if there are low levels of debt, consumers tend to spend more and save less.

Recommended: What is the Average Savings by Age?

Why Marginal Propensity to Save Matters

Using the data from MPS and MPC helps businesses, governments, and foreign policymakers determine how funds are allocated. For example, economists can assess this data to determine increases in government spending or investment spending, influencing savings numbers.

As for consumers, using the marginal propensity to save formula can help them make adjustments to their own spending habits. If their MPC is higher than their MPS, adjustments to consumption may need to be made.

How to Start Saving Money

While the way consumers spend helps the government and economists determine the best way to increase government spending, the way you choose to spend your money can help you set up a solid financial future. Carefully considering all of your spending options may get you on a path toward financial security. Being motivated to save money can have long-term benefits.

So if a windfall comes your way, you may want to consider carefully choosing how to spend those funds. While it’s tempting to use the money on a shopping spree, putting it in some type of savings account may be a better financial decision. After all, saving your extra disposable income can help build an emergency fund, avoid taking on debt, and accumulate a nest egg for your retirement.

Here are a few steps for getting started, even when it feels hard to save money:

Identifying Your Savings Goals

Do you have short-term goals like accumulating an emergency fund to pay for unexpected expenses? Or perhaps you want to save for a family vacation? Maybe you have a medium-term goal, such as paying for a wedding reception or a new kitchen renovation. Or would you like to save for retirement as a long-term goal? No matter your goals, you’ll want to have a clear idea of how much cash you need and by when.

First, decide on a goal date — when you want to have the money saved by. Then, divide the goal amount by the time frame, in months, to determine how much cash you need to stash away each month. Finally, decide where to keep the funds.

•   If your goal is short-term, you may want to consider putting your cash in a high-interest savings account or money market account. Either type of account is relatively low risk and is likely to be FDIC or NCUA insured, depending on the financial institution.

•   If the goals are more long-term, retirement accounts or brokerage accounts are worth considering since they may help your money grow.

Recommended: Take the guesswork out of saving for emergencies with our user-friendly emergency fund calculator.

Creating a Budget

It’s hard to track your money if you don’t know where it’s going. Creating and sticking to a budget is a great way to monitor your spending habits so you can stay on track.

•   To start, take note of your income and expenses for a month or two.

•   Next, create a monthly budget that reflects the average spending amounts for fixed expenses such as your mortgage and variable expenses such as eating out or clothes shopping. Also note money that goes towards savings.

•   If you determine you’re spending more than you earn, you may want to look for ways to cut back on your expenses, such as canceling subscriptions you don’t use. Or you could bring in more earnings by starting a side hustle or selling items that are still useful but that you don’t need.

Using a tool like SoFi or another digital tool makes it easy to track and categorize your expenses. It also helps you find ways to save and lets you monitor your progress toward your goals.

Recommended: Struggling to create a balanced budget? Try our 50/30/20 budget calculator for a simple solution.

Opening a Savings Account

When you receive an increase in your income, setting up automatic contributions to your savings or retirement accounts allows you to set aside extra money by automating your savings instead of having to manually transfer money each month. Look for an account with higher than average interest rate, typically found at online vs. traditional banks.

Interested in opening an online bank account? When you sign up for a SoFi Checking and Savings account with direct deposit, you’ll get a competitive annual percentage yield (APY), pay zero account fees, and enjoy an array of rewards, such as access to the Allpoint Network of 55,000+ fee-free ATMs globally. Qualifying accounts can even access their paycheck up to two days early.

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Can MPS be greater than 1?

The marginal propensity to save (MPS) cannot be greater than one since it is a change in savings, and that difference cannot be greater than one, nor less than zero.

How do you calculate the marginal propensity to save?

To calculate the MPS, or the marginal propensity to save, use the formula of change in savings divided by change in income.

What is the difference between average and marginal propensity to save?

The average propensity to save is defined as the ratio of total savings to total income. However, when talking about the marginal propensity to save, or the MPS, that is the ratio of change in savings to a change in income. The latter reflects a shift.

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